The invention relates to a self-supporting optical cable with a core comprising at least one optical conductor and a central member with several strength members disposed in a concentric reinforcing layer about this core and at a distance to it wherein these members form a compression-proof jacket, and an external protective jacket.
Several cables of this type are known in several types of implementation. It must be taken into consideration that optical conductors are extraordinarily sensitive to tensile loads, pressure, and bending loads. The strength members or the reinforcing layer therefore have the task to relieve in optimal manner the strain due to tensile and bending loads of the optical conductors encompassed by them. From the French Patent Application with the publication number 2 444 282 is known an ocean cable with optical conductors of high tensile and pressure strength which has a compression-proof rigid jacket. This jacket is formed of a multiplicity of profiled steel wires that are disposed so as to be laterally in contact with each other and whose height is greater than their width. Therefore the compression-proof jacket, and consequently the described cable, is very heavy and rigid. Such a cable is unsuitable as a self-supporting cable, in particular as an overhead line, and is therefore used only as an ocean cable.
An aerial cable with a tubular support member and optical conductors is known from Patent DE 33 19 370 A1. The optical conductors are herein inserted loosely into a central protective conduit. This protective conduit is surrounded by a closed jacket of resin which contains tension-proof fibers. This jacket has a diameter greater by a multiple than the diameter of the protective conduit for the optical conductors. If a soft resin is used for the jacket so that the cable remains flexible then the jacket is no longer compression-proof. If the resin is so hard that radial pressure loads can also be absorbed, a relatively rigid cable results which cannot be readily handled. Although this cable structure protects the optical conductors well, the optical conductors can be stretched or bent impressibly since their disposition in the protective conduits is not defined and can also not be checked. If a moderately large number of optical conductors is installed in such a cable they can disturb each other and place a mechanical stress on each other which leads to damages. The security of this cable construction is insufficient for the optical conductors and the cable is susceptible to interference.
A further optical cable which is said to avoid to above stated disadvantages is known according to Patent Application EP 150 768 A2 wherein the strength members are stranded around the optical conductors. Therein the strength and armouring members are said to be stranded around the core in a particular direction of turn and a length of turn to be calculated. Only when strictly adhering to this disposition are the optical fibers protected against tensile load. The formula given for the determination of turn length and twist diameter of the armouring members permits a theoretical determination. Important factors of influence such as physical constants and geometric data with different cable structures as well as adhesion between the individual cable layers cannot be determined mathematically and must therefore be determined experimentally. This causes considerable expenditures in the development of such cables and the appropriate experiments must be carried out anew with each change of the cable structure or the geometric shape. Furthermore, this cable structure does not protect the optical conductors disposed in the interior against pressure loads which can occur transversely to the longitudinal direction of the cable.